1. Field of the Invention
This invention relates to a method and an apparatus for continuous shaping of a carbon-fiber-reinforced plastic tube (hereinbelow, referred to as a CFRP). More particularly, it is concerned with a method and an apparatus adapted to be used for continuous shaping of a CFRP having thin wall thickness, light weight, long length and high mechanical strength, such as those used for constructive members of a large-scaled aeronautic and space structure.
2. Discussion of Background
As the method for continuous shaping of lengthy shaped products having a definite cross-sectional configuration such as fiber-reinforced plastic (FRP) tubes, in which the reinforcing fibers are impregnated with a thermosetting resin to be made a matrix, there has been well known the pulling method, by which actual production of insulating tubes, anti-corrosive tubes, and so forth of a large wall thickness using glass fibers as the reinforcing material, has been done heretofore.
FIG. 4 of the accompanying drawing shows the basic concept of the conventional pulling method and apparatus, which has been quoted from an unexamined Japanese Patent Publication No. 58467/1976 concerning a shaped product of a pipe.
In the drawing, a reference numeral 1 designates a mat of reinforcing fibers which are delivered out of a plurality of bobbins; a numeral 2 refers to a mandrel fixedly held between a mat delivering part and a hot die; a numeral 3 refers to an impregnating means for forcibly impregnating a resin on a laminate formed on the outer circumference of the mandrel in a matrix form; a reference numeral 4 denotes a preheater for heating the laminate impregnated with the resin (for the heating means, radio-frequency wave is used in this embodiment); a numeral 5 refers to the hot die for curing and shaping the impregnated resin; a numeral 6 refers to a pull-out drive mechanism for grasping the shaped product and continously moving the same in the rightward direction; and a numeral 7 designates a plastic tube as a shaped product to be moved to the right by means of the pull-out drive mechanism 6:
Explaining the method of shaping the tube in this embodiment, the mat of reinforcing fibers 1 to be delivered out of the bobbins is put on the mandrel to form a laminate of the mat on the outer circumference of it. Then, a resin is forcibly impregnated in the laminate, thereby obtaining a preshaped product. Thereafter, this preshaped product is caused to pass through the preheater 4 to heat the same, then the surplus amount of the impregnating resin is removed by the hot die 5, and, at the same time, external configuration of the preshaped product is regularized. Following this, the resin is cured to thereby obtain a predetermined shaped product 7. In this case, the shaped product 7 is grasped by the pulling mechanism 6 to obtain a pulling force in the right direction. This pulling mechanism comprises two grasping devices and is capable of exerting continuous pulling force by alternately grasping the product by the two grasping devices.
While the above-described embgdiment is to impregnate the mat after laminated with the resin, an Unexamined Japanese Patent Publications No. 96067/1978 and No. 124/1981 disclose methods for pull-out shaping of hollow tubes, which comprises winding on and around a mandrel a fiber strand impregnated with a thermosetting resin, and thereafter subjecting the resin-impregnated fiber strand to the pull-out shaping by the mandrel.
In addition, there has been a report made by W. B. Goldworthy et al. in "The 36th (1981) Annual Society of Plastics, Session 15-F, pages 1 to 6" concerning a shaping method which is characterized in that the shaped product and the mandrel are moved together by the pulling mechanism having two units of the grasping device, although this method uses an oven type curing means.
These conventional shaping methods as described in the preceding, however, are not able to sufficiently cope with shaping of the carbon-fiber-reinforced plastic tubes of light weight, thin thickness and long length, to be used for the constructive members of, for example, a large-scaled space structure, taking advantage of the superiority in relative strength and relative modulus of elasticity of carbon fibers as the reinforcing material. In more detail, the shaped products for such purpose are required to have their ultimate weight reduction in relation to their requisite mechanical strength, for which a strength sustaining factor, for example, of the shaped product with respect to the theoretical value (to be represented by "ROM %" in terms of reduction in thickness to 1 mm or less and precision in shaping) has to be improved. However, these conventional shaping methods did not take this ROM % into account.
Such conventional pull-out shaping method is primarily to obtain with high efficiency a thick shaped product, in which glass fibers are used as the reinforcing material. Therefore, if and when such conventional technique is to be directly applied in the practice of the precision-shaping of a product having thin thickness of 1 mm or less, using the reinforcing fibers of high modulus of elasticity (i.e. the fibers which are brittle and easily breakable) such as carbon fibers, there would inevitably take place considerable decrease in the strength sustaining factor (ROM %) which is dependent on the state of the reinforcing fibers such as breakage and disturbance in orientation of the reinforcing fibers, uneven distribution of the fibers, etc.; a mixing ratio between the fibers and the resin; and further the uniform curing property of the resin, and so forth. As the consequence of this, the value of the strength sustaining factor, in the case of the high precision and high performance products for use in the space structure, becomes not only innegligible, but also totally inadequate for shaping the carbon-fiber-reinforced plastic tubes having a wall thickness of 0.5 mm or less.
Describing this conventional shaping method for each and every process mechanism, there is, at first, a process step, in which the reinforcing fibers are delivered out of a bobbin stock in the form of fiber strand (hereinafter simply called "roving") and then the roving is wound on and around the mandrel after its being impregnated with a thermosetting resin, or the roving is impregnated with the resin after its being wound on and around the mandrel, following which they are forwarded to the subsequent preheating step. At any rate, the reinforcing fibers, in this case, come into direct contact with each of the process mechanism or are subjected to a forced bending. On account of this, when the carbon fiber is used as the reinforcing fibers, there tend to readily occur fuzzing (cracks in the fibers) and breakage of the fibers. Moreover, such resin impregnating means is difficult to control the fiber content V.sub.f (a volume fraction between the fibers and the resin), hence it is difficult to achieve the ultimate reduction in weight of the shaped product with respect to its required mechanical strength.
In addition, since a large number of bobbins are needed at the same time for supply of the reinforcing fibers in the form of roving, it is inevitable that a material feeding section of the process mechanism becomes large in its dimension and occupying area (space). Therefore, when such material feeding section is incorporated in the production line, there take place unavoidably various problems concerning the factory control, material control, and other managerial matters.
In the conventional curing and shaping step, a large amount of surplus thermosetting resin has to be removed, since this conventional method is primarily directed to obtain a thick shaped product in the main. For removal of such excess amount of resin, various measures were taken such that the squeezing angle in the squeezing section of the hot die for the curing and shaping process is made large, or multi-stage squeezing is carried out, which tends to cause the carbon fibers to be readily broken. In order to avoid the breakage of the carbon fibers, it is considered to reduce the squeezing angle. However, in a shaping method in which a large surplus amount of the resin has to be removed, resin removing efficiency will decrease. On the other hand, in a shaping method in which a small surplus amount of the resin is removed, there causes gellation of the resin staying in the squeezing section during shaping a long-sized product. This results in increase of viscosity and a reverse tension, which may cause the carbon fibers to be broken and reduction in the strength sustaining ratio (ROM %).
Incidentally, as the method for shaping such high performance carbon-fiber-reinforced plastic, in which more attention is paid to the strength sustaining factor (ROM %), there is a shaping method using a batch system which combines the filament winding and the autoclave curing. This method, however, is considerably inferior in its productivity for the large-scaled space structure, hence it cannot be adopted for the purpose of the present invention.